Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.87   4.757%   $258.6136   $258.61   $258.60   $258.60  
  Purchase #2 $69.51   5.448%   $73.2969   $73.30   $73.30   $73.30  
  Purchase #3 $108.87   13.510%   $123.5783   $123.58   $123.60   $123.60  
  Purchase #4 $209.65   6.425%   $223.12   $223.12   $223.10   $223.10  
  Purchase #5 $229.51   7.869%   $247.5701   $247.57   $247.55   $247.60  
  Purchase #6 $11.25   13.357%   $12.7527   $12.75   $12.75   $12.80  
  Purchase #7 $44.70   5.765%   $47.277   $47.28   $47.30   $47.30  
  7 purchase totals = $920.36       $986.2086   $986.21   $986.20   $986.30